Submitted by Adam Johnson / Harvey Mudd College on Mon, 10/03/2011 - 01:00
My Notes

This is an addendum to the Manganese Carbonyl experiment (linked below).  In this part of the experiment, students carry out high level quantum mechanical calculations of reactants, intermediates, and products in order to determine which of two possible structures is correct.

Learning Goals

A student will learn modern computational methods as applied to an organometallic complex

a student will apply the results of a computational experiment to a real synthesis

Equipment needs

The exercise is written assuming access to a WebMO cluster, but could be readily modified for use on a local Gaussian/Spartan environment.  There are two related activities that are not showing up below so I am linking them here:……

Implementation Notes

I have made this a required characterization method for my students who choose to do this experiment in my course.  As the theory required to get the "right" answer is high, I provide optimized input files and simply have the students calculate the energies, vibrations, and MOs.  This addendum is very strongly appealing for budding computational chemists, and is a good way for me to recruit joint thesis students to work on modeling inorganic systems for my research.  It is very helpful to have a computational chemist available to help with running the jobs the first time you do this, but it is not particularly taxing for the software.

Time Required
several hours for the computations, several more for analysis and writeup. This is done out of class.
Evaluation Methods

I usually have to work individually with students on this, but the payoff is high.  Once students see the light, they get really excited about it.  I look to make sure they are calculating the total energy of the reaction, have correctly identified the CO stretches and made some attempt to visualize the MOs.

Evaluation Results

students sometimes try to calcuate the reaction coordinate energy by only using the HOMO energy.  Students sometimes have a hard time finding the correct vibrational modes that relate to CO stretching

Creative Commons License
Attribution, Non-Commercial, Share Alike CC BY-NC-SA
Adam Johnson / Harvey Mudd College

I just uploaded a word doc and an excel sheet under the faculty only files that provide some DFT data (energies and CO stretching frequencies) and a preliminary interpretation of the reaction using DFT. I hope it helps anyone who wants to add this experiment to their repertoire during COVID-19.

Fri, 03/20/2020 - 17:38 Permalink
Adam Johnson / Harvey Mudd College

A savvy student noted that there was a potential mistake in the IR data for the trans isomer (and presumably for the trans cation). I reran the calculations to investigate and he was paritally right, so ht to JT for pointing this out. For a perfectly trans species, you would expect only one IR stretch for the carbonyls, since the symmetric stretch would not have IR intensity. The symmetric stretch is the one at 2100 cm-1 and its intensity is about 5% of the one at 2045 cm-1. This better matches the experimental spectrum for dppm 1.3 provided which does show a weak intensity symmetric stretch (that had gone unnoticed before). When I get a chance I will note this in the provided data above.


editied to add: the trans cation stretch at 2140 cm-1 is intense and the one at 2178 cm-1 is very weak (<2%).

Thu, 05/07/2020 - 15:17 Permalink